The present invention relates to a knock control method and apparatus for suppressing knocking and for increasing the torque of an internal-combustion engine.
When the compression ratio is high, the engine has a greater tendency to knock than when the compression ratio is low. Particularly, when the engine is running at a low or medium rotational speed and the throttle valve is almost wide open, the above-mentioned tendency of the engine to knock increases.
Therefore, it is necessary to suppress knocking in engines with a high compression ratio and in turbocharged engines under the above-mentioned engine operating condition. One conventional method for suppressing knocking in such engines is to supply an antiknock agent such as water or alcohol to an engine operating in a knock-development condition, i.e., in a condition wherein the engine has a great tendency to knock. At the same time, the ignition timing of the engine is advanced to Minimum advance for the Best Torque (MBT) so as to improve the torque characteristics thereof.
In this conventional method, however, since the ignition timing is advanced to MBT simultaneous with supply of the antiknock agent, there is a delay in the supply and transmission of the antiknock agent. This delay causes very loud knocks for several cycles of the engine operation.